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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 9  |  Issue : 3  |  Page : 243-247

Preoperative cone beam computed tomography evaluation of mandibular second and third molars in relation to the inferior alveolar canal


1 Department of Oral and Basic Clinical Sciences, Taibah University, Al-Madinah, Al Monwarah, KSA
2 Resident in Endodontics Saudi Board, King Abdulaziz University, Jeddah, KSA
3 Resident in Prosthodontics Saudi Board, Dar Al Uloom University, Riyadh, KSA
4 Dentist at Ministry of Health, Al-Madinah, Al Monawarah, KSA
5 Intern in Taibah University, Al-Madinah, Al Monawarah, KSA

Date of Submission30-Jun-2020
Date of Decision23-Aug-2020
Date of Acceptance10-Sep-2020
Date of Web Publication07-Nov-2020

Correspondence Address:
Ebtihal H Zain-Alabdeen
Department of Oral and Basic Clinical Sciences, College of Dentistry, Taibah University, Al-Madinah, Al Monwarah
KSA
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/sjhs.sjhs_127_20

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  Abstract 


Objective: The aim is to evaluate the location and proximity of second and third molars roots to the inferior alveolar canal (IAC) and demographic factors associated with these proximities. Materials and Methods: Cone beam computed tomography scans were evaluated for 292 roots of 146 teeth from 40 patients. A radiologist read, measured, and evaluated the vertical and horizontal positions of the roots of the second and third molars in relation to the IAC. Results: No significant differences were found between the third molar roots and neighboring second molar roots in the closeness to the IAC. The most common horizontal relation was “roots above IAC” (54%) followed by “roots lingual to IAC” (41.78%), “roots buccal to IAC” (3.42%), and “IAC between the roots” (0.68%). No significant differences in second and third molar roots and their contrasting teeth in the proximity to IAC. The older age group had significantly higher vertical measurements between third molar roots and IAC. There were significantly larger vertical measurements in the right third molar roots to IAC in males than females. Conclusions: These anatomical relationships are important clinical knowledge to avoid potential surgical injury to the inferior alveolar nerve.

Keywords: Cone beam computed tomography, inferior alveolar canal, second molar, third molar


How to cite this article:
Zain-Alabdeen EH, Alhazmi RA, Alsaedi RN, Aloufi AA, Alahmady OA. Preoperative cone beam computed tomography evaluation of mandibular second and third molars in relation to the inferior alveolar canal. Saudi J Health Sci 2020;9:243-7

How to cite this URL:
Zain-Alabdeen EH, Alhazmi RA, Alsaedi RN, Aloufi AA, Alahmady OA. Preoperative cone beam computed tomography evaluation of mandibular second and third molars in relation to the inferior alveolar canal. Saudi J Health Sci [serial online] 2020 [cited 2021 Jan 19];9:243-7. Available from: https://www.saudijhealthsci.org/text.asp?2020/9/3/243/300287




  Introduction Top


Surgical extraction of impacted third molars may be the most frequent procedure in oral surgery. Damage to the inferior alveolar nerve (IAN) is a typical complication of the procedure due to the proximity of the third molar to the inferior alveolar canal (IAC), with incidence rates reported to be 1%–22%.[1] The second molar has also been shown to have a close relation to the IAC, with the potential risk of IAN injury.[2]

Furthermore, high percentage of the endodontic surgeries and treatments showed that mandibular second and third molars root apices due its proximity to the IAC can cause nerve injury.[3]

Previously, surgeons depended solely on panoramic radiography to evaluate the proximity of the third molars to the IAC, through specific radiographic risk signs (darkening of third molar roots, narrowing of the canal, and diversion of canal, absence of corticalization between mandibular third molar and the IAC),[4],[5]

However, because panoramic radiography is a two-dimensional imaging tool, the images can be distorted or overlapped.[6] Nakayama et al.[7] suggested that this may lead clinicians to misinterpret the results or make incorrect judgments.

The introduction of cone-beam computed tomography (CBCT) allowed for the creation of multiplanar images as in computed tomography (CT) but with less radiation exposure. Surgeons began using this device to evaluate the proximity between the third molar and the IAC. Some studies suggested that contact between the IAC and the mandibular third molar root apices, revealed with CBCT, predicted potential risk for IAN exposure or injury during extraction.[7],[8] Nonetheless, one study found no significant difference in the sensitivity and specificity between panoramic radiography and CBCT in predicting IAN exposure.[9] Another investigation proposed that spiral CT images enhanced visualization of the relation of the tooth to the IAC, potentially providing a higher level of intrasurgical safety and safeguarding the interests of both surgeon and patient.[10] Liu et al.[11] suggested that the limitations of the panoramic radiograph in depicting the true 3D morphology of the IAC are recognized and that 3D imaging such as CT or CBCT is more precise.

CBCT is used to provide a radiographic surgical guide to the relationship of the lower posterior teeth roots.[12],[13] Some CBCT studies classified the relationship between the site of the root of the tooth and the mandibular canal into four groups. These studies found that the risk of damage to the IAN is increased if the third molar intersects with the mandibular canal, particularly on its buccal side.[14]

These studies were focused on n the risk of third molar extraction on the IAN injury. However, in Saudi Arabia, extraction is highly indicated for the second molar because of the high prevalence of caries.[15] To our knowledge, only two studies in the Saudi population[16],[17] have been performed to evaluate the proximity of the second molar to the IAN and the potential of other demographic risk factors; both studies compared the second molar to anterior teeth, which are further from the IAC. This study will be focusing on comparing the proximity of the second molar to the IAC compared to third molars, which have been reported previously to be the most proximal to the IAC.[7]

The null hypothesis for this study is that there is no significant difference in vertical measurements between the second and third molars apices to the IAC; in addition to that, we will examine this measurement according to age, gender, and mandible sides using CBCT. Moreover, to detect the most common horizontal location (above, buccal, lingual, or interradicular) of the second and third molars in relation to the IAC, and most proximal roots (mesial or distal) to the IAC.


  Materials and Methods Top


The sample size was calculated as 36 on the basis of the following parameters: 95% confidence interval, 5% margin of error, 33% estimated prevalence, a Z-score of 1.96.

We applied the following formula:

In this study a total population size of 40 were obtained from the clinical records.

The study was revised by the Taibah University College of Dentistry Research Ethics Committee and was approved unconditionally; consent document is not requested, the radiograph used in this study was anonymous, and the confidentiality of the patient preserved.

This is a cross-sectional radiographic study. We included all patients referred between April 2016 and April 2017 from the surgery clinic at University Dental Clinic to the radiology Department for CBCT scans to detect the proximity of the second or third mandibular molars to the IAC. CBCT scans were reclaimed from the records of the Carestream R4 Clinical and Practice Management Software database (CareStream Health, Rochester, NY, USA) of Taibah University Dental college and were acquired with a CS 9300 PREMIUM 3D CBCT device (CareStream, Rochester, NY, USA) set at 73 kV and 12 mA. A radiologist with >7 years' experience read, measured, and evaluated the vertical and horizontal position of the second and third molars in relation to the IAC. The data were collected from cross-sectional, axial, and coronal views, and measurements were taken using CareStream 3D Imaging Software, NY, USA. The cross-sectional slices were used to visualize the buccolingual position of the canal; measurements were then obtained from this view for roots of the second and third mandibular molars for each patient. After aligning the coronal and sagittal planes with the long axis of each root, and the root is fully seen, the shortest distance from the tip of the root apex surface to the nearest outer surface of the cortical boundary of the IAC was measured for each root.

The radiologist performed the measurements for ten selected cases twice within a 1-week time interval. A paired t-test showed no significant difference between the first and second readings.

For the horizontal relation, the same cross-sectional view we see if the root is above the IAC, buccal, lingual, or some were between IAC.

Inclusion and exclusion criteria

All fully erupted second or third mandibular molars of male and female patients were included. The exclusion criteria were as follows: all remaining roots of mandibular second and third molars; inability to identify the cortication of IAC on the radiograph; displacement of the mandibular second and third molars due to pathology, such as cysts or tumors; and mandibular second and third molars without an opposing tooth. The reason for the latter exclusion was to prevent wide variation from drifting of an erupted third molar with root displacement.

After the inclusion and exclusion criteria were applied, a total of 146 mandibular second and third molars were included in the study.

Study variables

Study variables included age, gender, vertical relation (distance from the mesial root to IAC, distance from the distal root to IAC), and horizontal variables (root above IAC, root buccal to IAC, root lingual to IAC, IAC between mesial and distal roots of the molar). A sample vertical measurement of the distal root of the third molar to the roof of the IAC and the horizontal relation are shown in [Figure 1].
Figure 1: Cross-sectional view of the: Vertical measurement of the third molar distal root in relation to the inferior alveolar canal is (3.7 mm), the horizontal relation: Roots above the inferior alveolar canal

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Statistical analysis

The data were imported to Stata 16 (StataCorp LLC, macOS, TX, USA) for analysis. Descriptive and frequency statistics were used for the horizontal relationships of the roots to the IAC; Independent t-tests were used to compare means of vertical measurements from the roots to IAC, between males and females, right and left sides, and age groups.


  Results Top


The sample consisted of 23 (57.5%) females and 17 (42.5%) males. Their age ranged from 19 to 60 years, with a mean of 32.22 years and a median of 29 years.

[Table 1] shows that 79 of 146 teeth “mesial and distal roots” (54.1%) were located above the IAC, the next common horizontal relation being teeth that were lingual to the IAC (41.78%), and the least common two relations being teeth that were buccal to the IAC (3.42%) and the IAC being between the roots of the teeth (0.68%). [Table 2] shows that the mesial root of the left third molar was the most common proximal root to the IAC (45.45%). The extent of proximity varied from intruding on the IAC (negative value) to 2 mm proximal to it. The second most common proximal root to the IAC was the mesial root of the right third molar (41.18%).
Table 1: Frequency and percentages of horizontal relation of the teeth to the inferior alveolar canal

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Table 2: Frequency and percentages of the proximity of the third and second molars to the inferior alveolar canal

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The mean difference in the vertical relation between the right and left molars was tested for significance; no significant difference was found in mean vertical measurements between the right and left roots in relation to the IAC. At a P = 0.05, there was no significant difference the vertical measurements of the roots to IAC between the third and second molar, the difference ranged from −0.89 mm to a maximum of 0.47 mm.

The difference in the vertical measurements means between two age groups (19–30 years) and (31–60) years were tested for significance; both the right and left third molars had significantly higher mean measurements in the older age group compared to the younger age group [Figure 2].
Figure 2: Bar chart showing vertical relation of tooth roots to the inferior alveolar canal for two age group. D: Distal, M: Mesial

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When the difference in mean vertical measurements between males and females was examined, it revealed significantly larger measurements in the mesial and distal roots of the right third molar in males than in the same molar in females [Figure 3].
Figure 3: Bar chart showing vertical relation of tooth roots to the inferior alveolar canal for males and females. D: Distal, M: Mesial

Click here to view



  Discussion Top


Ranking among the most regular of maxillofacial and oral surgeries is the removal of the mandibular third molar. Injury to the IAN as a result of this excision can be consequential for patients, as it may alter the performance of the stomatognathic system and thus their quality of life. Anatomically, the principal contributing factor to IAN injury is the horizontal and vertical relationship between the mandibular canal and associated third molars.[18] In this study, we included the mandibular second molar due to its proximity to the IAC[16] and its high rate of extraction in Saudi.[15]

In this study, the null hypothesis was accepted, and there was no significant difference between the closeness of the root apices of the second and third molars roots apices to the IAC; the previous two studies done in Saudi were comparing second molars to anterior teeth,[16],[17] together with Aksoy et al. study[19] all agreed that the distance from root apices of mandibular second molars to IAC, decreases when moving to more anterior teeth. In this study, we compared the second molars with the only tooth posterior to it “third molars,” it was found that the second molar apices are slightly further from IAC; nevertheless, this distance was not significantly different from the third molar proximity to the IAC; therefore, both teeth may equally require CBCT imaging before surgery.

In this study, the most mutual horizontal relation of both the second and third molars were roots above the IAC (54%), followed by roots lingual to the IAC (41.78%), roots buccal to the IAC (3.42%), and the IAC between the roots (0.68%). This classification from most common to least common was compatible with another study at slightly different proportions.[18]

Our results showed that the mesial root of the left third molar is the most usual proximal root to the IAC. This finding contradicts the result of a study by Aksoy et al.,[19] who reported that the distal roots of the right third molars have the lowest mean distance to the IAC (1.93 mm), followed by the distal root of the left third molars (2.54 mm). However, these numbers depend on tooth angulations.

Our study also demonstrated no significant difference in the mean vertical measurements between the right and left root in relation to the IAC. Similarly, a study by Bürklein et al.[20] found that there were no significant differences in location (right or left) of the teeth in relation to the IAC.

Our results showed that the older patient group had significantly higher vertical measurements of the roots in relation to the IAC compared to the younger age group. This was compatible with three studies, Bürklein et al.[20] and Shokry et al.[17] who both found significantly shorter closeness from the IAC to the root apices in patients younger than 35 years compared to older patients. Moreover, Kovisto et al. who reported that the distance between the IAC and root apices increased with age.[21]

The vertical dimensions were generally higher in males than in females in the present study. This result is compatible with findings of other studies in which the distance from the IAC to the apices of posterior molars was reported to be smaller in women than in men.[19],[20],[22] Furthermore, in Shokry et al. study, they found that the vertical distance in males at the first premolar region is significantly higher than females, and they attributed that to the increase of the overall vertical dimension of the male mandible.[17]

Limitations of this study are that the sample included patients of different ethnicities and therefore, the anatomical findings cannot be generalized.


  Conclusions Top


This study showed that there is no significant difference in the closeness to the IAC between the second and third mandibular molars and disclosed horizontal relations between the roots of the second and third molars to the IAC. These anatomical relationships are important clinical knowledge to avoid potential surgical injury to the IAN.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Aksoy U, Orhan K. Risk factor in endodontic treatment: Topographic evaluation of mandibular posterior teeth and lingual cortical plate using cone beam computed tomography (CT). Med Sci Monit 2018;24:7508-16.  Back to cited text no. 3
    
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